SEVERE THUNDERSTORM - a thunderstorm which produces:

winds greater than 58 mph

damage to trees, telephone/utility poles or any structure

tornado

SEVERE THUNDERSTORM WATCH - issued by the Storm Prediction Center when severe thunderstorms are possible in and near the watch area (box). The watch is issued for a large area and is usually in effect for several hours.

SEVERE THUNDERSTORM WARNING - issued by your local NWS Forecast Office when severe weather is imminent or occurring and is usually in effect for about an hour.